The Fast Saves feature automates the process of saving a document. In theory, this sounds great. However, as well as saving any changes to the document, it also retains any text that you’ve ‘deleted’ from a document. This partly explains why documents that use fast save can bloat to very large file sizes.
If you are concerned about deleted text remaining in your documents, you should perform the following steps:
On the Tools menu, click Options.
Select the Save tab.
Click to clear the Allow fast saves check box. Click OK.